Conventionally, a stud-type tracking wheel, generally called a cam follower, is a sort of roller bearing in which an outer ring thick in radial dimension fits over a stud for free rotation through more than one rolling element of needle interposed between them. The outer ring serves as a tracking wheel coming into rolling-contact with a race on any mating member including a cam and so on, while the stud has any joint including a thread, abutment, and so on to easily fasten it to any associated member.
Many sorts of stud-type roller bearing with tracking wheel have been heretofore used for the cam follower. A prior stud-type roller bearing with tracking wheel is disclosed in, for example Japanese Patent Laid-Open No. 1998-196648 in which an inner race or stud installed in an outer race for rotation has a shaft extending out of the outer race in axial direction, which is used to support the roller bearing on any associated member in a cantilevered fashion. The stud is made with a lubrication hole to accommodate a lubricating plug therein. The lubrication hole communicates with passages to allow lubricant to reach the raceways on which the roller rolls. The lubrication hole also communicates with a hexagonal socket that is made on an axial end of the stud. Moreover, another lubrication hole to accommodate the lubricating plug therein is provided at an externally threaded end of the stud. The prior stud-type roller bearing with tracking wheel constructed as stated earlier is easier to mount and/or demount it from any other machines such as machine tool or the like as well as possible to produce it at low cost.
In recent years, the small stud-type roller bearing with tracking wheel has been frequently seen in diverse machines and instruments and needed having a built-in lubricating plug that makes it possible to replenish the rollers with lubricant. Nevertheless, the stud-type roller bearing with tracking wheel, especially, small stud-type roller bearing, because of the stud with less redundancy on it for installation of a grease nipple, is very tough to carry out replenishment of lubricant. A previous approach to the resolution of the problem as stated just above is the stud-type roller bearing with tracking wheel in which the lubricating plug is installed in the lubrication hole in the stud, which is disclosed in the senior application of the common assignment recited earlier.
With the prior stud-type roller bearing with tracking wheel where the lubricating plug is installed in the lubrication hole in the stud, however, since the lubricating plug is made in a bumpily intricate configuration, the mold to produce the lubricating plug has to become sophisticated in cavity contour, thereby very difficult to form the mold. This results in the major problem that the prior lubricating plug costs too high to qualify for the small stud-type roller bearing with tracking wheel. With the prior stud-type roller bearing with tracking wheel constructed as recited earlier, in addition, the lubricating plug is provided therein a hollow chamber extending straight in axial direction. In alignment of the end face of the lubricating plug with the lubrication hole lying normal to the axis of the stud, there is a practical issue that an outlet of the hollow chamber made open on the end face of the lubricating plug must be determined in the precise position relative to the lubrication hole in the stud.
With the prior small stud-type roller bearing with tracking wheel, especially, small stud-type roller bearing in which the stud is not more than 10 mm in diameter d in FIG. 3, there is less in room to install the grease nipple there and the grease nipple itself has to be made as small as possible. Thus, the prior small stud-type roller bearing with tracking wheel gets substantially impossible to replenish it with lubricant. In the prior small stud-type roller bearing with tracking wheel in which there are provided a lubrication hole as shown at 10 in FIG. 3 and a lubricant passage shown at 22 in FIG. 3 extending normal to the lubrication hole, a plug such as ball or the like is pressed into the lubrication hole lest any contaminant including foreign matter, debris, and so on invades or any oily material leaks out through the lubrication hole after the lubricant such as grease and the like has been once applied into the race through the lubrication hole.